1. Field of the Invention
The present invention relates to reflective type semiconductor display devices. More particularly, the invention relates to a reflective type active matrix liquid crystal display device using a display medium. The reflective type semiconductor display device of the invention, however, may use any of other display mediums with which modulation in optical property can be made responsive to a voltage applied to the display medium (for example, an elecroluminescent device, etc.).
2. Description of the Prior Arts
Recently, advancement has being made for the technology to manufacture a semiconductor device, such as with thin film transistors (TFTs), on an inexpensive glass substrate. The reason of this lies in increase of demand for active matrix liquid crystal display devices (liquid crystal panels).
The active matrix liquid crystal panel has pixel TFTs which are arranged in respective pixels in number of from several hundreds to several millions to form TFT array so that electric charge can be controlled of input to and output from each pixel electrode through TFT switch function.
The TFT array includes thin film transistors utilizing amorphous silicon formed over a glass substrate.
Meanwhile, there has been recent realization of active matrix liquid crystal display devices utilizing a quartz substrate to form polycrystalline silicon thin film transistors. This structure can afford to form driver circuits for driving TFTs on the same substrate as the TFT array.
Furthermore, there is a known technology of utilizing laser annealing or the like, in order to form thin film transistors using a crystalline silicon film on a glass substrate. This technology, if utilized, can integrate the TFT array together with the driver circuits on a glass substrate.
In recent years, active matrix liquid crystal display devices. have been frequently utilized on notebook personal computers. The personal computers require a multi-tone liquid crystal display device to simultaneously start a plurality of software or process images fetched from a digital camera.
Furthermore, recently there has been recent demand for an active matrix liquid crystal display device that is small in size but high in definition, resolution and image quality, as become popular the portable intelligence terminals, mobile computers, car navigators.
The drive to the active matrix liquid crystal device used on the portable intelligence terminal or mobile computer is based on a battery, hence requiring low power consumption. Under such a circumstance, the reflective type active matrix liquid crystal devices drawn attentions toward the mobile computer application and the like. The reflective type active matrix liquid crystal display devices are low in power consumption because, as one reason, of the unnecessity of backlight, unlike the transparent type active matrix liquid crystal display devices.
It is needless to say that the active matrix liquid crystal display devices for mobile computers or the like has to be made as small as possible. There is a recent attempt to form driver circuits to drive the TFT array on a same substrate as the TFT array.
Furthermore, attentions are drawn to an SOP (System On Panel) structure built on a same substrate with control circuits, including a processor circuit, memory circuit, A/D (D/A) converter circuit, correction circuit (gamma correction circuit) and pulse oscillation circuit, besides the driver circuits (shift register circuit, buffer circuit, etc.) for driving pixel TFTs constituting the TFT array.
One example of an active matrix liquid crystal display device structure is herein shown in FIG. 9. FIG. 9 shows only an active matrix substrate for an active matrix liquid crystal display device, wherein 901 is an active matrix substrate, 902 and 903 are source drivers, 904 and 905 are gate drivers, and 906 is TFT array. Incidentally, the active matrix substrate 901 basically uses an insulation substrate such as a glass or quartz substrate.
The active matrix substrate shown in FIG. 9 has two source drivers and two gate drivers. This is due to a structure to drive odd-numbered source signal lines by the source driver 902 and drive even-numbered source signal lines by the source driver 903. Also, the gate drivers on left and right are formed in a redundant structure.
Note that the TFT array 906 includes a plurality of pixel TFTs arranged in a matrix form.
Also, the source drivers 902 and 903 includes a shift register circuit, level shifter circuit, buffer circuit and sampling circuit. The level shifter circuit is a circuit to amplify a drive voltage.
For example, where the shift register circuit is on 10V drive and the buffer circuit is 16V drive, voltage has to be converted by the level shifter circuit. There are cases that the shift register circuit be substituted by a combination of counter and decoder circuits.
On the other hand, the gate driver includes a shift register circuit, level shifter circuit, buffer circuit and so on.
Meanwhile, for more complicated structures of active matrix liquid crystal display devices, consideration is made to place other logic circuits in positions as shown at 907 to 910 in FIG. 9. The other logic circuits include a complicate circuit such as a control circuit and processor circuit, and a broad occupation-area circuit such as a memory circuit. It is expected that the total occupation area results in large.
As discussed above, it is a general practice to arrange, on one insulation substrate, a TFT array 906, source drivers 902 and 903, gate drivers 904 and 905, and other logic circuits. Consequently, the occupation area of other than the TFT array has to be reduced to a size as small as possible, in order to secure a display area maximally enlarged for realizing high definition, high resolution and high image quality.
In the structure shown in FIG. 9, however, it is difficult to reduce the occupation area of other than the TFT array. This is one of factors to obstruct the size reduction for the active matrix liquid crystal display devices.
Under such situations, Japanese Laid-Open Patent Publication 10-104663 discloses a structure that, in forming a reflective type active matrix liquid crystal display device including a TFT array, driver circuits and other control circuits on one insulation substrate, the driver circuits and the other control circuits are formed within a region of the TFT array. The Japanese Laid-Open Patent Publication 10-104663 corresponds to a pending U.S. patent application Ser. No. 08/937,377, an entire disclosure of which are incorporated herein by reference.
In the Japanese Laid-Open Patent Publication 10-104663, there are disclosed the TFTs of the driver and control circuits are placed underneath a reflective pixel electrode connected to pixel TFTs of the TFT array.
Here, FIG. 11 shows FIG. 8A of the Japanese Laid-Open patent Publication 10-104663. There is shown in FIG. 11 a sectional view of an active matrix substrate according to a certain embodiment of the Japanese Laid-Open Patent Publication 10-104663. FIG. 11 depicts that interconnects for the driver and control circuits are formed in a layer different from a layer having source and drain electrodes of TFTs for the driver and control circuits (the interconnect denoted at A in FIG. 11). In this structure, however, clock and data signals flowing through the driver and control circuits are passed through the interconnect shown at A. This results in occurrence of electrical noise on the interconnects shown at A, due to the clock and data signals. In brief, it is unavoidable that the electrical noise caused on the interconnect A have adverse effects on pixel electrodes. This leads to disturbance in display images due to such electrical noise, thus making difficult to obtain favorable images.